The first successful experiments which demonstrated the KCD invention were made using highly purified (research grade) xenon at approximately 25 atmospheres pressure. Some of the advantages of using xenon are:
1. Xenon has the highest atomic number of the available noble gases. This yields the highest x-ray attenuation coefficient at diagnostic x-ray energies and the highest photoelectric interaction probability.
2. Xenon has a low mobility for its ions which means higher electric fields must be used for a given kinestatic velocity. This reduces the relative field distortions caused by the space charge of the ions produced during the detection of the x-ray beam.
3. Several other advantages exist for a xenon detection medium it has a relatively low W-value (average energy to produce an ion pair), it is a monatomic molecule (polyatomic media are slowly consumed during irradiation) and it has a high dielectric constant.
However, xenon also possesses disadvantages when used in a KCD including:
1. A high fluorescent yield (0.85) and a relatively high K-fluorescence energy (30 keV) which produces a scatter "halo" around the point spread function and a reduced spatial resolution.
2. A further reduced resolution in the scanning direction caused by the generation of multiple positive ionic species not in chemical equilibrium and having disparate mobilities.
The second disadvantage was discovered from the increasing width of the point spread function for a pulsed x-ray beam from a slit, as a slit was moved away from the signal collection region. Other possible sources of the effect such as ionic diffusion, space charge, grid shielding inefficiency and electric field nonuniformity cannot adequately explain the observations.